1. Field of the Invention
The present invention relates to a positioning-indexing control device for an inverter apparatus and more particularly to positioning-indexing control device for inverter apparatus with an induction motor connected thereto as its load.
2. Description of the Prior Art
As the control device of this type the one as shown in FIG. 1 has previously been proposed.
Referring to FIG. 1, reference numeral 1 denotes a three-phase power source, 2 denotes a rectifying circuit formed of a diode, thyristor, and the like for rectifying the alternating current supplied by the power source 1, and 3 denotes a filter for smoothing the d.c. voltage from the rectifying circuit 2. And, 4 denotes an inverter apparatus formed of switching elements such as a transistor for converting the d.c. voltage from the rectifying circuit 2 into a pulse-width modulated variable-frequency a.c. voltage, 5 denotes an induction motor as the load of the inverter apparatus 4 (hereinafter to be referred to as a motor), 6 denotes a speed detector for detecting the rotational speed of the motor 5, 7 denotes a pulse generator for generating a mark pulse P.sub.mo which indicates a rotational position of the motor 5 and a positional pulse P.sub.m, 8 denotes a speed command circuit for providing a standard speed v.sub.r as a speed command for the motor 5, and 9 denotes a speed detecting circuit for counting a speed signal v.sub.m output by the speed detector 6 and outputting a speed detected value v.sub.mr and a signal v.sub.ma which indicates that a designated speed has been reached. Further, 10 denotes a pulse detecting circuit for counting the mark pulse P.sub.mo from the pulse generator 7 and the positional pulse P.sub.m and outputting a position detected value P.sub.mr and an in-position signal P.sub.i, 11 denotes a slip-frequency computing unit for computing a deviation .DELTA.v of the speed detected value v.sub.mr from the standard speed v.sub.r, 12 denotes a voltage-to-pulse converter in response to the sum of the deviation .DELTA.v from the slip-frequency computing unit 11 and the speed detected value v.sub.mr from the speed detecting circuit 9, v.sub.mr +.DELTA.v, for outputting a pulse P.sub.o whose frequency is proportional to a frequency command f.sub.o, 13 denotes a voltage command circuit in response to the frequency command f.sub.o from the voltage-to-pulse converter 12 for outputting a voltage command V.sub.o which corresponds to the voltage-frequency characteristic of the motor 5, and 14 denotes a waveform generating circuit in response to the pulse P.sub.o and the voltage command V.sub.o for outputting a signal V.sub.r indicating the reference voltage waveform for PWM control. And, 15 denotes a voltage detecting circuit for detecting a signal V.sub.I indicating an output voltage of the inverter apparatus 4, 16 denotes a control circuit for outputting a signal S.sub.I for operating the inverter apparatus 4 in such a way that the deviation between the signal V.sub.r from the waveform generating circuit 14 and the signal V.sub.I is minimized, and 17 denotes an external output circuit for outputting the signal v.sub.ma indicating that the designated speed has been reached from the circuit 9 and the in-position signal P.sub.i from the circuit 10 to an external interface.
Now, with reference to the waveform diagram in FIG. 2, description will be made on the operation for stopping the rotation of the motor 5 at a predetermined position. Referring to FIG. 2, (a) represents a waveform of a speed command v.sub.r, (b) that of a command for stopping at a predetermined position, (c) that of a signal v.sub.ma indicating that a designated speed has been reached, (d) that of a mark pulse P.sub.mo, which is output at the rate of one pulse per rotation of the motor, and (e) represents a waveform of an in-position signal P.sub.i indicating completion of stoppage of the motor 5.
If the command for stopping at a predetermined position is input at the time point t.sub.1, the speed command circuit 8 reduces the standard speed v.sub.r from v.sub.r0 to v.sub.r1, an orient speed (approximately, 100 to 200 rpm). At the time point t.sub.2, the speed detecting circuit 9 detects that the rotational speed of the motor 5 has reached the standard speed v.sub.r1 and outputs the signal v.sub.ma indicating that the designated speed has been reached. At the time point t.sub.3, the mark pulse P.sub.mo is output from the pulse generator 7, whereupon counting of the positional pulse P.sub.m is started. At the time point t.sub.4, the position detected value P.sub.mr indicates that the motor 5 has reached the position within approximately 180.degree. of the aimed stop position, and so, the speed command circuit 8 reduces the standard speed v.sub.r to v.sub.r2, a creep speed (approximately, 20 to 30 rpm). At the time point t.sub.5, the motor 5 reaches the position within approximately 30.degree. of the aimed stop position, and therefore, the control loop formed of the speed command circuit 8--the waveform generating circuit 14 is switched to a positional loop, whereby the standard speed v.sub.r becomes the speed to be determined by the gain in the positional loop. At the time point t.sub. 6, the motor 5 reaches the aimed stop position, and so, an in-position signal P.sub.i is output from the pulse detecting circuit 10 indicating that the motor 5 has stopped at the aimed stop position.
In such a device of the prior art, it has only been possible to designate one stop position at one time of the command for stopping at a predetermined position. And so, if it was desired to stop a motor at different positions, a command for stopping at another predetermined position had to be set and input after a previous command for stopping at a position was released. It therefore followed that the motor had to rotate more than one full rotation each time it operated at such a repeated command. Taking a case, by way of example, where cutting work is carried out with an attachment fitted to a spindle driven by a motor, it was impossible, after the attachment was stopped at a certain position and cutting was made at that position, to continue that cutting work with the attachment rotated and stopped within a full rotation of the previous position. Thus, there has been such a disadvantage that the function to stop the spindle at desired positions in the prior art was unable to meet multiple purposes.